Microcapsules Containing Curable Siloxanes

ABSTRACT

Aqueous suspensions of silicate shell microcapsules are disclosed wherein a first portion of the silicate shell micro-capsules contain an organopolysiloxane having at least two alkenyl groups and a hydrosilylation catalyst as Part A of a curable siloxane composition, and a second portion of the silicate shell microcapsules contain an organohydrogensiloxane as Part B of the curable siloxane composition.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Patent Application No.61/222,200, as filed on Jul. 1, 2009.

TECHNICAL FIELD

This disclosure relates to aqueous suspensions of silicate shellmicrocapsules wherein a first portion of the silicate shellmicrocapsules contain an organopolysiloxane having at least two alkenylgroups and a hydrosilylation catalyst as Part A of a curable siloxanecomposition, and a second portion of the silicate shell microcapsulescontain an organohydrogensiloxane as Part B of the curable siloxanecomposition.

BACKGROUND

Water-based hydrosilylation curable siloxane compositions are commonlyused in many industrial processes, for example for paper coatingapplications. Typically, they are two component emulsion systems where afirst emulsion contains a hydrosilylation catalyst and a vinylterminated polydimethylsiloxane (PDMS) while the other emulsion containsan organohydrogensiloxane. When the two emulsion parts are mixedtogether, a composition ripening phenomena may occur from the diffusionof the components from the various emulsion particles resulting inpremature curing of the composition. As a result a cure inhibitor istypically added in the mix in order to extend the “bath life” of thecoating compositions. The final cure of the mix is obtained by theevaporation of the cure inhibitor at high temperature following acoating process.

Thus, a need exists to provide hydrosilylation curable siloxanecompositions for use in water based systems that eliminate the need forthe addition of cure inhibitors to extend bath life of the coatingcompositions, and allow for low temperature cure.

SUMMARY

The present inventors have discovered microencapsulated hydrosilylationcurable siloxane compositions that cure at room temperature, showextended bath life times, and also have lower extractable content thancorresponding emulsion based compositions.

The present disclosure provides aqueous suspensions of silicate shellmicrocapsules of a two part curable siloxane composition. Morespecifically, the aqueous suspension contains a mixture of silicateshell microcapsules wherein a portion of the silicate shellmicrocapsules contain as a core the first part (Part A) of a curablesiloxane composition while another portion of the microcapsules containthe second part (Part B) of the curable siloxane composition. When thetwo part curable compositions are released from the microcapsules undercertain conditions, the two compositions react to form a cured siloxanecomposition.

DETAILED DESCRIPTION

The curable siloxane composition encapsulated in silicate shellmicrocapsules of the present aqueous suspensions may be anyhydrosilylation curable siloxane composition. Such hydrosilylationcurable siloxane compositions typically involve the reaction of anorganopolysiloxane containing alkenyl groups with anorganohydrogensiloxane in the presence of a hydrosilylation catalyst.

A portion of the silicate shell microcapsules in the present aqueoussuspensions contain as a core, one part (Part A) of a curablecomposition. Part A of the curable siloxane composition contains atleast two components;

-   -   a) an organopolysiloxane having at least two silicon-bonded        alkenyl groups per molecule, and    -   b) a hydrosilylation catalyst.        A second portion of the microcapsules in the aqueous suspension        contains the second part (Part B) of the curable siloxane        composition. Part B of the curable siloxane composition contains        at least one    -   c) organohydrogensiloxane.

In one embodiment, Part B of the curable siloxane composition contains acombination of both components a) and c), that is a mixture of the anorganopolysiloxane having at least two silicon-bonded alkenyl groups permolecule and the organohydrogensiloxane.

In a further embodiment, the amounts of components a) and c) used inPart B of the curable siloxane composition is such so as to provide amolar ratio of SiH/alkenyl group that varies from 3 to 10.

Each component is described in detail as follows.

a) The Organopolysiloxane Having at Least Two Silicon-Bonded AlkenylGroups

Organopolysiloxanes are polymers containing siloxy units independentlyselected from (R₃SiO_(1/2)), (R₂SiO_(2/2)), (RSiO_(3/2)), or (SiO_(4/2))siloxy units, where R is typically a hydrocarbon group. These siloxyunits can be combined in various manners to form cyclic, linear, orbranched structures. The chemical and physical properties of theresulting polymeric structures can vary. For example organopolysiloxanescan be volatile fluids, low viscosity fluids, high viscosityfluids/gums, elastomers, rubbers, or resins.

Component a) may be selected from any organopolysiloxane, or mixture oforganopolysiloxanes comprising at least two siloxy units represented bythe formula R²R_(m)SiO_((4-m)/2)

wherein

R is an hydrocarbon group containing 1 to 20 carbon atoms,

R² is an alkenyl group containing 2 to 12 carbon atoms, and

m is zero to 2.

The R² alkenyl groups of Component a) are exemplified by vinyl, allyl,3-butenyl, 4-pentenyl, 5-hexenyl, 6-heptenyl, 7-octenyl, 8-nonenyl,9-decenyl, 10-undecenyl, 4,7-octadienyl, 5,8-nonadienyl, 5,9-decadienyl,6,11-dodecadienyl and 4,8-nonadienyl.

The R² alkenyl group may be present on any mono, di, or tri siloxy unitin the organopolysiloxane, for example; (R²R₂SiO_(1/2)), (R²RSiO_(2/2)),or (R²SiO_(3/2)); as well as in combination with other siloxy units notcontaining an R² substituent, such as (R₃SiO_(1/2)), (R²SiO_(2/2)),(RSiO_(3/2)), or (SiO_(4/2)) siloxy units where R is a hydrocarboncontaining 1 to 20 carbons, alternatively an alkyl group containing 1 to12 carbons, alternatively an alkyl group containing 1 to 6 carbons oralternatively methyl; providing there are at least two R² substituentsin the organopolysiloxane. The monovalent hydrocarbon group R havingfrom 1 to 20 carbon atoms is exemplified by alkyl groups such as:methyl, ethyl, propyl, butyl, hexyl, octyl, and decyl; cycloaliphaticgroups such as cyclohexyl; aryl groups such as phenyl, tolyl, and xylyl,and aralkyl groups such as benzyl and phenylethyl.

Representative, non-limiting, examples of such organopolysiloxanessuitable as component a) include those having the average formula;

(R₂R²SiO_(1/2))_(v)(R₂SiO_(2/2))_(x)

(R²R²SiO_(1/2))_(v)(R₂SiO_(2/2))_(x)(R²RSiO_(2/2))_(y)

(R²R²SiO_(1/2))_(v)(R₂SiO_(2/2))_(x)(RSiO_(3/2))_(z)

(R₂R²SiO_(1/2))_(v)(R₂SiO_(2/2))_(x)(RSiO_(3/2))_(z)(SiO_(4/2))_(w)

(R₂R²SiO_(1/2))_(v)(SiO₂)_(w)(R₂SiO)_(x)

(R³SiO_(1/2))_(v)(R₂SiO)_(x)(R²RSiO_(2/2))_(y)

(R³SiO_(1/2))_(v)(R₂SiO)_(x)(R²RSiO)_(y)

(R₃SiO_(1/2))_(v)(R₂SiO)_(x)(R²RSiO)_(y)(RSiO_(3/2))_(z)

(R³SiO_(1/2))_(v)(R₂SiO)_(x)(R²RSiO)_(y)(SiO₂)_(w)

(R₃SiO_(1/2))_(v)(R₂SiO)_(x)(R²RSiO)_(y)(SiO₂)_(w)(RSiO_(3/2))_(z)

(R³SiO_(1/2))_(v)(R₂SiO)_(x)(R²SiO_(3/2))_(z)

-   -   where v≧2, w≧0, x≧0, y≧2, and z is ≧0,    -   R and R² are as defined above.

Component a) may also be a mixture of any of the aforementionedorganopolysiloxanes. The molecular weights may vary, and are notlimiting. However, when molecular weights become too high or if theorganopolysiloxane is a solid, it may be difficult to handle orincorporate the organopolysiloxane in the microcapsules as a corematerial. Thus, it may be desirable to dilute component a) in a suitablesolvent or lower molecular weight fluid, such as a less viscous siliconefluid. Typically the viscosity at 25° C. of component a) or dispersionof component a) in another fluid may vary from

1 to 10,000 mPa·s,

-   -   alternatively, 50 to 1000 mPa·s, or        -   alternatively, 100 to 1000 mPa·s.

Component a) may be selected from the group consisting oftrimethylsiloxy-terminated polydimethylsiloxane-polymethylvinylsiloxanecopolymers, vinyldimethylsiloxy-terminatedpolydimethylsiloxane-polymethylvinylsiloxane copolymers,trimethylsiloxy-terminatedpolydimethylsiloxane-polymethylhexenylsiloxane copolymers,hexenyldimethylsiloxy-terminatedpolydimethylsiloxane-polymethylhexenylsiloxane copolymers,trimethylsiloxy-terminated polymethylvinylsiloxane polymers,trimethylsiloxy-terminated polymethylhexenylsiloxane polymers,vinyldimethylsiloxy-terminated polydimethylsiloxane polymers, andhexenyldimethylsiloxy-terminated polydimethylsiloxane polymers, eachhaving a degree of polymerization of from 10 to 300, or alternativelyhaving a viscosity at 25° C. of 10 to 1000 mPa·s.

Alternatively component a) may be selected from vinyl functionalendblocked polydimethylsiloxanes (vinyl siloxanes) or hexenyl functionalendblocked polydimethylsiloxanes (hexenyl siloxanes), such as thosehaving the average formula;

CH₂═CH(Me)₂SiO[Me₂SiO]_(x)Si(Me)₂CH═CH₂

CH₂═CH—(CH₂)₄-(Me)₂SiO[Me₂SiO]_(x)Si(Me)₂-(CH₂)₄—CH═CH₂

Me₃SiO[(Me)₂SiO]_(X′)[CH₂═CH(Me)SiO]_(x″)SiMe₃

wherein Me is methyl,

-   -   x′ 0, alternatively x is 0 to 200, alternatively x is 10 to 150,    -   x″ 2, alternatively x″ is 2 to 50, alternatively x″ is 2 to 10.

Vinyl or hexenyl functional polydimethylsiloxanes are known, and thereare many commercially available. Representative, non-limiting examplesinclude DOW CORNING® fluids; SFD 128, DC4-2764, DC2-7891, DC2-7754,DC2-7891, and DC2-7463, SFD-117, SFD-119, SFD 120, SFD 129, DC5-8709,LV, 2-7038, DC 2-7892, 2-7287, 2-7463, and dihexenyl terminal DC7692,DC7697 (Dow Corning Corporation, Midland, Mich.).

b) The Hydrosilylation Catalyst

Component b) is a hydrosilylation catalyst. The hydrosilylation catalystmay be any suitable Group VIII metal based catalyst selected from aplatinum, rhodium, iridium, palladium or ruthenium. Group VIII groupmetal containing catalysts useful to catalyze curing of the presentcompositions can be any of those known to catalyze reactions of siliconbonded hydrogen atoms with silicon bonded unsaturated hydrocarbongroups. The preferred Group VIII metal for use as a catalyst to effectcure of the present compositions by hydrosilylation is a platinum basedcatalyst. Some preferred platinum based hydrosilylation catalysts forcuring the present composition are platinum metal, platinum compoundsand platinum complexes.

Suitable platinum catalysts are described in U.S. Pat. No. 2,823,218(commonly referred to as “Speier's catalyst) and U.S. Pat. No.3,923,705. The platinum catalyst may be “Karstedt's catalyst”, which isdescribed in Karstedt's U.S. Pat. Nos. 3,715,334 and 3,814,730.Karstedt's catalyst is a platinum divinyl tetramethyl disiloxane complextypically containing about one-weight percent of platinum in a solventsuch as toluene. Alternatively the platinum catalyst may be a reactionproduct of chloroplatinic acid and an organosilicon compound containingterminal aliphatic unsaturation, as described in U.S. Pat. No.3,419,593. Alternatively, the hydrosilyation catalyst is a neutralizedcomplex of platinum chloride and divinyl tetramethyl disiloxane, asdescribed in U.S. Pat. No. 5,175,325.

Other hydrosilylation catalysts suitable for use in the presentinvention include for example rhodium catalysts such as [Rh(O₂CCH₃)₂]₂,Rh(O₂CCH₃)₃, Rh₂(C₈H₁₅O₂)₄, Rh(C₅H₇O₂)₃, Rh(C₅H₇O₂)(CO)₂,Rh(CO)[Ph₃P](C₅H₇O₂), RhX⁴ ₃[(R³)₂S]₃, (R² ₃P)₂Rh(CO)X⁴, (R²₃P)₂Rh(CO)H, Rh₂X⁴ ₂Y² ₄, H_(a)Rh_(b)olefin_(c)Cl_(d),Rh(O(CO)R³)_(3-n)(OH)_(n) where X⁴ is hydrogen, chlorine, bromine oriodine, Y² is an alkyl group, such as methyl or ethyl, CO, C₈H₁₄ or 0.5C₈H₁₂, R³ is an alkyl radical, cycloalkyl radical or aryl radical and R²is an alkyl radical an aryl radical or an oxygen substituted radical, ais 0 or 1, b is 1 or 2, c is a whole number from 1 to 4 inclusive and dis 2, 3 or 4, n is 0 or 1. Any suitable iridium catalysts such asIr(OOCCH₃)₃, Ir(C₅H₇O₂)₃, [Ir(Z⁴)(En)₂]₂, or (Ir(Z⁴)(Dien)]₂, where Z⁴is chlorine, bromine, iodine, or alkoxy, En is an olefin and Dien iscyclooctadiene may also be used.

Further suitable hydrosilylation catalysts are described in, forexample, U.S. Pat. Nos. 3,159,601; 3,220,972; 3,296,291; 3,516,946;3,989,668; 4,784,879; 5,036,117; and 5,175,325 and EP 0 347 895 B.

The hydrosilylation catalyst may be added to Part A in an amountequivalent to as little as 0.001 part by weight of elemental platinumgroup metal, per one million parts (ppm) of the total curable siloxanecomposition (that is Parts A and B combined). Typically, theconcentration of the hydrosilylation catalyst in the curable siloxanecomposition is that capable of providing the equivalent of at least 1part per million of elemental platinum group metal. A catalystconcentration providing the equivalent of 1 to 500, alternatively 50 to500, alternatively 50 to 200 parts per million of elemental platinumgroup metal may be used.

c) The Organohydrogensiloxane

Component c) is an organohydrogensiloxane having an average of greaterthan two silicon bonded hydrogen atoms per molecule. As used herein, anorganohydrogensiloxane is any organopolysiloxane containing asilicon-bonded hydrogen atom (SiH).

Organohydrogensiloxanes are organopolysiloxanes having at least one SiHcontaining siloxy unit, that is at least one siloxy unit in theorganopolysiloxane has the formula (R₂HSiO_(1/2)), (RHSiO_(2/2)), or(HSiO_(3/2)). Thus, the organohydrogensiloxanes useful in the presentinvention may comprise any number of (R₃SiO_(1/2)), (R₂SiO_(2/2)),(RSiO_(3/2)), (R₂HSiO_(1/2)), (RHSiO_(2/2)), (HSiO_(3/2)) or (SiO_(4/2))siloxy units, providing there are on average at least two SiH siloxyunits in the molecule. Component c) can be a single linear or branchedorganohydrogensiloxane or a combination comprising two or more linear orbranched organohydrogensiloxanes that differ in at least one of thefollowing properties; structure, viscosity, average molecular weight,siloxane units, and sequence. There are no particular restrictions onthe molecular weight of the organohydrogensiloxane, but typically theviscosity of the organohydrogensiloxane at 25° C. is from 3 to 10,000mPa·s, alternatively 3 to 1,000 mPa·s, or alternatively 10 to 500 mP·s.

The amount of SiH units present in the organohydrogensiloxane may vary,providing there are at least two SiH units per organohydrogensiloxanemolecule. The amount of SiH units present in the organohydrogensiloxaneis expressed herein as % SiH which is the weight percent of hydrogen inthe organohydrogensiloxane. Typically, the % SiH varies from 0.01 to10%, alternatively from 0.1 to 5%, or alternatively from 0.5 to 2%.

The organohydrogensiloxane may comprise the average formula;

(R³ ₃SiO_(1/2))_(a)(R⁴ ₂SiO_(2/2))_(b)(R⁴HSiO_(2/2))_(c) wherein

R³ is hydrogen or R⁴,

R⁴ is a monovalent hydrocarbon group having from 1 to 10 carbon atoms

-   -   a≧2,    -   b≧0, alternatively b=1 to 500, alternatively b=1 to 200,    -   c≧2, alternatively c=2 to 200, alternatively c=2 to 100.

R⁴ may be a substituted or unsubstituted aliphatic or aromatichydrocarbyl. Monovalent unsubstituted aliphatic hydrocarbyls areexemplified by, but not limited to alkyl groups such as methyl, ethyl,propyl, pentyl, octyl, undecyl, and octadecyl and cycloalkyl groups suchas cyclohexyl. Monovalent substituted aliphatic hydrocarbyls areexemplified by, but not limited to halogenated alkyl groups such aschloromethyl, 3-chloropropyl, and 3,3,3-trifluoropropyl. The aromatichydrocarbon group is exemplified by, but not limited to, phenyl, tolyl,xylyl, benzyl, styryl, and 2-phenylethyl.

In another aspect, the organohydrogensiloxane may contain additionalsiloxy units and have the average formula

(R³ ₃SiO_(1/2))_(a)(R⁴₂SiO_(2/2))_(b)(R⁴HSiO_(2/2))_(c)(R⁴SiO_(3/2))_(d),

(R³ ₃SiO_(1/2))_(a)(R⁴ ₂SiO_(2/2))_(b)(R⁴HSiO_(2/2))_(c)(SiO_(4/2))_(d),

(R³₃SiO_(1/2))_(a)(R⁴HSiO_(2/2))_(b)(R⁴HSiO_(2/2))_(c)(SiO_(4/2))_(d)(R⁴SiO_(3/2))_(e)

or any mixture thereof,

where

R³ is hydrogen or R⁴,

R⁴ is a monovalent hydrocarbyl,

and a≧2, b≧0, c≧2, d≧0, and e is ≧0.

In another embodiment, the organohydrogensiloxane is selected from adimethyl, methyl-hydrogen polysiloxane having the average formula;

(CH₃)₃SiO[(CH₃)₂SiO]_(b)[(CH₃)HSiO]_(c)Si(CH₃)₃

-   -   where b≧0, alternatively, b=1 to 200, alternatively b=1 to 100,        -   and c≧2, alternatively, c=2 to 100, alternatively c=2 to 50.

Methods for preparing organohydrogensiloxanes are well known, and manyare sold commercially.

The amounts of components a) and c) used in the oil phases to preparethe separate microcapsules containing Parts A and B may vary. However,the amounts used in the total siloxane composition may be adjusted toachieve a desired molar ratio of the SiH groups of component c) to thealkenyl groups present in component a). Typically, sufficient amount ofcomponent c) is used to provide a molar ratio of SiH to alkenyl groupsof component a) to be greater than 1, alternatively in the range of 1 to10, alternatively 1 to 4, alternatively 2 to 3.

The suspensions of silicate shell microcapsules may be prepared by anyprocess known in the art. In general, there are two processes ortechniques commonly used to prepare silicate shell microcapsules. Thefirst technique involves an in-situ polymerization of a silicateprecursor (sometimes referred to as a sol-gel process), after firstmixing the silicate precursor with an oil phase. Representative, nonlimiting examples of the in-situ process are those taught in U.S. Pat.No. 6,159,453, U.S. Pat. No. 6,238,650, U.S. Pat. No. 6,303,149, and WO2005/009604.

The second technique involves an ex-situ process, where thepolymerization of a silicate precursor occurs via an emulsionpolymerization process. Representative, non-limiting examples of suchtechniques are taught in WO03/066209.

In one embodiment, the silicate shell microcapsules are prepared by;

-   -   I) mixing an oil phase containing Part A or Part B of the        curable siloxane composition and an aqueous solution of a        cationic surfactant to form an oil in water emulsion,    -   II) adding a water reactive silicon compound comprising a        tetraalkoxysilane to the oil in water emulsion,    -   III) polymerizing the tetraalkoxysilane at the oil/water        interface of the emulsion to form a microcapsule having a core        containing either Part A or Part B of the curable siloxane        composition and a silicate shell,    -   IV) combining the microcapsules containing Part A of the curable        siloxane composition with the microcapsules containing Part B of        the curable siloxane composition.        In this embodiment, the above process is performed twice, once        to prepare microcapsules containing Part A of the curable        siloxane composition, and a second to prepare the microcapsules        containing Part B of the curable siloxane composition. The        resulting suspensions of microcapsules are then combined to form        a mixture of the microcapsules in an aqueous suspension.

Part A of the curable siloxane composition contains components a) and b)as described above. Typically, Part A contains component a) andsufficient hydrosilylation catalyst to effect the hydrosilylationreaction. For example, Part A might contain 96-98 weight percent ofcomponent a) and 2-4 weight percent of a solution of platinum catalyst(typically containing 0.52 wt % elemental Pt) as component b).

Part B of the curable siloxane composition contains component c). Part Bmay contain additional components, as further described below. In oneembodiment, Part B of the curable siloxane composition contains bothcomponents a) and c), that is a mixture of the organopolysiloxane havingat least two alkenyl groups and the organohydrogensiloxane.

When components a) and c) are combined to form Part B, the amounts mayvary, depending on the desired objectives for curing the siloxanecomposition. Typically the amounts range from 50-94 weight percent ofcomponent a) and 6-50 weight percent component c).

In a further embodiment, the amounts of components a) and c) used inPart B of the curable siloxane composition is such so as to provide amolar ratio of SiH/alkenyl group that varies from 3 to 10, oralternatively from 4 to 9, or alternatively from 5 to 7. The presentinventors have found this ratio provides curable siloxane compositionsthat readily cure as thin films, such as in various coatingapplications, yet provide adequate storage stability as an aqueoussuspension.

While not wishing to be bound by any theory, the present inventorsbelieve combining components a) and c) in the ratios described above inPart B of the curable siloxane composition in the microcapsulesuspensions allows for a partial reaction between theorganohydrogensiloxane and organopolysiloxane containing alkenyl groups.It is speculated that some small amounts of the hydrosilylation catalystfrom Part A may permeate through the microcapsules and suspension andcause some reaction between components a) and c), while still present inthe microcapsules. Upon eventually rupturing the microcapsules, such aswhen allowing thin films of the suspension to dry, Parts A and B reactmore efficiently to form cured siloxane compositions. Thus, the presentinventors have discovered an optimum ratio in this embodiment to provideexcellent cure rates of the siloxane compositions, while alsomaintaining storage stabilities of such compositions in an aqueous basedmedium.

As used herein, “oil phase” encompasses Part A or Part B of the curablesiloxane composition. Typically, the oil phase is a liquid when formingthe oil in water emulsion. The oil phase may contain additional powders,pigments, drugs, inks, organic, silicone, or fluorocarbon based oils incombination with either Part A or Part B. However, in cosmeticapplications, additional silicone oils are preferred. The oil phase mayalso contain any solvent or diluent, which may be added for the purposeof solubilizing solid hydrophobic compounds to create a liquid oil phaseduring formation of the emulsion.

The oil phase containing either Part A or B of the curable siloxanecomposition may contain other components, either silicone or organicbased components, that are substantially soluble with the other oilphase components, and conversely, is substantially insoluble in water.Thus, other typical emollient components can include: silicones, such asvolatile siloxanes, polydimethylsiloxane fluids, high molecular weight(i.e. M_(w)>1000) siloxanes, including silicone elastomers and resins;organic compounds such as, hydrocarbon oils, waxes, and emollients.

The oil phase containing either Part A or B of the curable siloxanecomposition may contain other components known as “burst aides”. As usedherein, “burst aid” encompasses any compound, or mixture of compoundsadded to the oil phase for the purpose of initiating temperaturecontrolled release of the encapsulated core material. The burst aids maybe selected from volatile hydrophobic organic or siloxane compounds.Burst aids might be volatile linear hydrocarbons, including but notlimited to, pentane, hexane, heptane, octane, nonane; volatile cyclichydrocarbons such as cyclopentane, cyclohexane, cycloheptane,cyclooctane; volatile branched hydrocarbons such as isohexane,isoheptane, isooctane, isodecane, isododecane; volatile linearsiloxanes, including but not limited to, hexamethyldisiloxane,decamethyltetrasiloxane; volatile cyclic siloxanes such asoctamethylcyclotetrasiloxane, decamethylcyclopentasiloxane,dodecylmethylcyclohexasiloxane. Alternatively, the burst aid may beselected from those known in art as “blowing agents”.

The oil phase containing either Part A or B of the curable siloxanecomposition is mixed with an aqueous solution of a cationic surfactantto form an oil in water emulsion.

Cationic surfactants useful in this invention might be quaternaryammonium hydroxides such as octyl trimethyl ammonium hydroxide, dodecyltrimethyl ammonium hydroxide, hexadecyl trimethyl ammonium hydroxide,octyl dimethyl benzyl ammonium hydroxide, decyl dimethyl benzyl ammoniumhydroxide, didodecyl dimethyl ammonium hydroxide, dioctadecyl dimethylammonium hydroxide, tallow trimethyl ammonium hydroxide and cocotrimethyl ammonium hydroxide as well as corresponding salts of thesematerials, fatty amines and fatty acid amides and their salts, basicpyridinium compounds, quaternary ammonium bases of benzimidazolines andpolypropanolpolyethanol amines but is not limited to this list ofcationic surfactants. A preferred cationic surfactant is cetyl trimethylammonium chloride or bromide.

For purposes of this disclosure, the cationic surfactant may be selectedfrom an amphoteric surfactant such as cocamidopropyl betaine,cocamidopropyl hydroxysulfate, cocobetaine, sodium cocoamidoacetate,cocodimethyl betaine, N-coco-3-aminobutyric acid compounds but is notlimited to this list of amphoteric surfactants.

The above surfactants may be used individually or in combination. Thecationic or amphoteric surfactant is dissolved in water and theresulting aqueous solution used as a component in aqueous or continuousphase of the oil in water emulsion of step I).

Although not wishing to be bound by any theory, the present inventorsbelieve the use of a cationic or amphoteric surfactant promotescondensation and polymerisation of the tetraalkoxysilane, as describedbelow, at the interface of the emulsified droplets of the oil phase,leading to non-diffusive microcapsules. The tetraalkoxysilane hydrolyzesand condenses upon reacting in the emulsion. The anionically chargedhydrolysis product is attracted to the cationic or amphoteric surfactantat the interface where it forms the silicon based polymer shell.

The concentration of the cationic surfactant during the formation of theoil in water emulsion should be between 0.1% and 0.3% by weight of theoil phase concentration used. Typically, the use of low levels ofcationic or amphoteric surfactant during emulsification of the oil phaseand reaction with the alkoxysilane leads to microcapsules which are moreresistant to diffusion or leaching of the oil phase from themicrocapsules.

Auxiliary surfactants, and in particular nonionic surfactants, may beadded during the formation of the oil in water emulsion. Suitablenon-ionic surfactants are; polyoxyalkylene alkyl ethers such aspolyethylene glycol long chain (12-14C) alkyl ether, polyoxyalkylenesorbitan ethers, polyoxyalkylene alkoxylate esters, polyoxyalkylenealkylphenol ethers, ethylene glycol propylene glycol copolymers,polyvinyl alcohol and alkylpolysaccharides, for example as described inU.S. Pat. No. 5,035,832 but is not limited to this list of non-ionicsurfactants.

The aqueous solution of the cationic or amphoteric surfactant maycontain additional/optional components, providing they are watersoluble. For example a water-miscible organic solvent such as an alcoholmay be added. Furthermore, other water soluble ingredients that arecommonly used in personal care formulations may be added to the aqueousphase. Such ingredients include additional surfactants, thickeners,preservatives, antimicrobial, and water soluble actives and fragrances.

The oil phase and aqueous solution of the cationic or amphotericsurfactant are mixed together to form an oil in water emulsion. Mixingand emulsion formation may occur using any known techniques in theemulsion art. Typically, the oil phase and aqueous solution of thecationic or amphoteric surfactant are combined using simple stirringtechniques to form an emulsion. Particle size of the oil in wateremulsion may then be reduced before addition of the tetraalkoxysilane byany of the known in the art emulsification device. Useful emulsificationdevices in this invention can be homogenizer, sonolator, rotor-statorturbines, colloid mill, microfluidizer, blades, helix and combinationthereof but is not limited to this list of emulsification devices. Thisfurther processing step reduces the particle size of the startingcationic oil in water emulsion to values ranging from 0.2 to 500micrometers, with typical particle sizes ranging between 0.5 micrometersand 100 micrometers.

The weight ratio of oil phase containing either Part A or B of thecurable siloxane composition to aqueous phase in the emulsion cangenerally be between 40:1 and 1:50, although the higher proportions ofaqueous phase are economically disadvantageous particularly when forminga suspension of microcapsules. Usually the weight ratio of oil phase toaqueous phase is between 2:1 and 1:3. If the oil phase composition ishighly viscous, a phase inversion process can be used in which the oilphase is mixed with surfactant and a small amount of water, for example2.5 to 10% by weight based on the oil phase, forming a water-in-oilemulsion which inverts to an oil-in-water emulsion as it is sheared.Further water can then be added to dilute the emulsion to the requiredconcentration.

In one embodiment, the density of the oil phase to the aqueous phase inthe emulsion is approximately the same, that is the densities are“matched”, alternatively the densities of each are within 2%,alternatively 1%, or alternatively within 0.5%

The second and third steps of the present process involve adding a waterreactive silicon compound comprising tetraalkoxysilane, wherein eachalkoxy group contains 1 to 4 carbons, alternatively 1 to 2 carbons, tothe oil in water emulsion, and polymerizing the tetraalkoxysilane at theoil/water interface of the emulsion. Although not wishing to be bound byany theory, the present inventors believe the third step effects an“ex-situ emulsion polymerization” by which the tetraalkoxysilaneprecursor hydrolyzes and condenses at the oil/water interface leading tothe formation of core-shell microcapsules via a phase transfer of theprecursors.

The tetraalkoxysilane, such as tetraethoxysilane (TEOS), can be used inmonomeric form or as a liquid partial condensate or oligomer. Thetetraalkoxysilane can be used in conjunction with one or more otherwater-reactive silicon compound having at least two, preferably at least3, Si—OH groups or hydrolysable groups bonded to silicon, for example analkyltrialkoxysilane such as methyltrimethoxysilane or a liquidcondensate/oligomer of an alkyltrialkoxysilane. Hydrolysable groups canfor example be alkoxy or acyloxy groups bonded to silicon. The waterreactive silicon compound can for example comprise 50-100% by weighttetraalkoxysilane and 0-50% trialkoxysilane. The alkyl and alkoxy groupsin the tetraalkoxysilanes or other silanes preferably contain 1 to 4carbon atoms, most preferably 1 or 2 carbon atoms. Thetetraalkoxysilane, and other water-reactive silicon compound If used,hydrolyses and condenses to form a network polymer, that is a3-dimensional network of silicon-based material, around the emulsifieddroplets of either Part A or Part B of the curable siloxane composition.The water-reactive silicon compound typically consists of at least 75%,or alternatively 90-100% tetraalkoxysilane. The tetraalkoxysilaneprovides the shell of impermeable microcapsules, forming a 3-dimensionalnetwork consisting substantially of SiO_(4/2) units.

The water reactive silicon compound may also comprise an alkoxysilanehaving other organofunctional groups such as a quaternized substitutedalkyl group. One preferred type of quaternary alkoxysilane has theformula (CH₃O)₃SiCH₂CH₂CH₂N⁺(CH₃)₂(CH₂)₁₇CH₃Cl⁻.

The water reactive silicon compound is added to the oil in wateremulsion (containing either Part A or B) as an undiluted liquid or as asolution in an organic solvent or in an emulsion form. The waterreactive silicon compound and the oil in water emulsion are mixed duringaddition. The tetraalkoxysilane in the water reactive silicon compoundsubsequently polymerizes to form the silicon-based polymer shell on thesurface of the emulsified droplets. Mixing is typically effected withstirring techniques. Common stirring techniques are typically sufficientto maintain the particle size of the starting oil in water emulsionwhile allowing the tetraalkoxysilane to polymerize and condense at theoil water interface

The amount of tetraalkoxysilane in the water reactive silicon compoundadded in step II typically ranges from 6/1 to 1/13, alternatively from1.2/1 to 1/7.3, alternatively from 1.3 to 1/6.1 based on the weightamount of oil phase present in the emulsion.

Alternatively, the amount of tetraalkoxysilane added in step II may beexpressed as a weight percent of the oil in water emulsion. The weightpercent of the tetraalkoxysilane added to the oil in water emulsion isat least 2 weight percent of the emulsion, alternatively at least 5weight percent of the emulsion, alternatively at least 7 weight percentof the emulsion, alternatively at least 10 weight percent of theemulsion, or alternatively at least 12 weight percent of the emulsion.

The polymerization of the water reactive silicon compound at theoil/water interface typically is a condensation reaction which may beconducted at acidic, neutral or basic pH. The condensation reaction isgenerally carried out at ambient temperature and pressure, but can becarried out at increased temperature, for example up to 95° C., andincreased or decreased pressure, for example under vacuum to strip thevolatile alcohol produced during the condensation reaction.

Any catalyst known to promote the polymerization of the water reactivesilicon compound may be added to step III to form the shell of themicrocapsule. The catalyst is preferably an oil soluble organic metalcompound, for example an organic tin compound, particularly an organotincompound such as a diorganotin diester, for example dimethyl tindi(neodecanoate), dibutyl tin dilaurate or dibutyl tin diacetate, oralternatively a tin carboxylate such as stannous octoate, or an organictitanium compound such as tetrabutyl titanate. An organotin catalyst canfor example be used at 0.05 to 2% by weight based on the water reactivesilicon compound. An organotin catalyst has the advantage of effectivecatalysis at neutral pH. The catalyst is typically mixed with the oilphase components before it is emulsified, since this promotescondensation of the water reactive silicon compound at the surface ofthe emulsified oil phase droplets. A catalyst can alternatively be addedto the emulsion before the addition of the water-reactive siliconcompound, or simultaneously with the water-reactive silicon compound, orafter the addition of the water-reactive silicon compound to harden andmake more impervious the shell of silicon-based polymer which has beenformed. Encapsulation can however be achieved without catalyst. Thecatalyst, when used, can be added undiluted, or as a solution in anorganic solvent such as a hydrocarbon, alcohol or ketone, or as amulti-phase system such as an emulsion or suspension.

The presence of colloidal silicate particles in the suspension ofsilicate shell microcapsules may limit the storage stability of thesesuspensions. Such colloid silicate particles may be considered as a sideproduct in the tetraalkoxysilane polymerization reaction to produce thesilicate shell microcapsule. The storage stability of suspensions ofsilicate shell microcapsules may be improved by reducing the amount ofcolloidal silicate particles in the suspension, or alternatively, arerendered non-reactive by the addition of a colloidal silicatesequestering agent. As used herein “a colloidal silicate sequesteringagent” refers to any compound or material that when added to thesilicate shell microcapsule suspension which also contains colloidsilica particles, interacts with the colloidal silicate particles insuch a manner so as to prevent their reaction or coagulation. Techniquesfor removing colloidal silicate particles and various colloidal silicatesequestering agents are further disclosed in U.S. Application No.61/096,397.

The colloidal silicate sequestering agent may be an organofunctionalsilane. In one embodiment, the organofunctional silane is a quatfunctional trialkoxysilane. Representative, non-limiting examples ofsuitable quat functional trialkoxysilanes include Dow Corning®Q9-6346—Cetrimoniumpropyltrimethoxysilane Chloride.

The colloidal silicate sequestering agent may be a silicone polyether.Silicone polyethers are commercially available. Representative,non-limiting examples of suitable silicone polyethers include DowCorning® 190, 193, and 2-5657.

EXAMPLES

These examples are intended to illustrate the invention to one ofordinary skill in the art and should not be interpreted as limiting thescope of the invention set forth in the claims. All measurements andexperiments were conducted at 23° C., unless indicated otherwise.

Materials Used as Part A—Catalyst Blend

Com- Abbreviated ponent Description Name a)Dimethylvinylsiloxy-terminated VINYL polydimethylsiloxane, SILOXANEViscosity = 300-600 cP (mPa · s) at 25° C. vinyl content = 0.45% (w/w)b) Karstedt catalyst (CAS Registry No. 684789-22) CATALYST1,3-Diethenyl-1,1,3,3-Tetramethyldisiloxane Complexes of Platinumdispersed in VINYL SILOXANE, to contain 0.52 wt % elemental Pt.

Materials Used as Part B—Base Blend

Abbreviated Component Chemical Name Name a)Dimethylvinylsiloxy-terminated VINYL polydimethylsiloxane, SILOXANEViscosity = 300-600 cP (mPa · s) at 25° C. vinyl content = 0.45% (w/w)c) Trimethylsiloxy-terminated, dimethyl- SiH methylhydrogenpolysiloxane, having a SILOXANE viscosity = 5 cP (mPa · s) at 25° C. andcontaining 0.795% SiHThe viscosities of the Vinyl Siloxane and SiH Siloxane were measured at23° C. according to Dow Corning CTM 0050 using a Brookfield RotationalViscometer with Spindle RVF #2 AT 20 RPM).

Example 1 (Comparative) Preparation of an Emulsion Containing as an OilPhase Part A of the Curable Siloxane

A first emulsion containing as an oil phase Part A of the curablesiloxane composition was prepared by mixing 45 g of VINYL SILOXANE, 1.4g of the CATALYST, 4 g of Laureth-23, and 3 g of Pareth-3. Then, 16 g ofwater was added and mixed with a Hauschild SpeedMixer DAC 150 FVZ for 20seconds. The emulsion was then progressively diluted by the addition ofwater to obtain a solids content of 30%. The resulting emulsion had anaverage volume particle size of (Dv 0.5)=3.7 micrometers. The pH wasadjusted to 3.7 by addition of 2.5M HCl.

Preparation of an Emulsion Containing as an Oil Phase Part B of theCurable Siloxane

A second emulsion containing as an oil phase Part B of the curablesiloxane was prepared in a similar manner by first mixing 40 g of theVINYL SILOXANE, 5 g of the SiH SILOXANE, 4 g of Laureth-23, and 3 g ofPareth-3. Then, 8 g of water was added and mixed with a HauschildSpeedMixer DAC 150 FVZ has been utilised for 20 seconds. The emulsionwas then progressively diluted with water in order to obtain a solidcontent of 30%. The resulting emulsion had an average volume particlesize of (Dv 0.5)=3.8 micrometers. The pH was adjusted to 3.7 by additionof HCl.

The emulsions containing Parts A and B are then mixed together at a 1/1w/w ratio.

Example 2 Preparation of Suspensions of Microcapsules Containing Part Aof the Curable Siloxane Composition.

A suspension of microcapsules containing Part A of the curable siloxanecomposition was prepared by first dissolving 3.35 g of cetyl trimethylammonium chloride (CTAC) in 791.9 g of water. Then, a blend of 675.6 gVINYL SILOXANE and 21 g the CATALYST was added with mixing to theCTAC/water mixture to form an O/W emulsion. In this particular case anUltra-Turrax T25 Basic was utilised for 180 seconds at 9500 rpm. Theresulting emulsion was then subjected to further shearing using an APV1000 Homogeniser at a pressure of 700 bars to produce a fine 0/Wemulsion having an average particle size (Dv 0.9) below 15 μm. The pH ofthe resulting emulsion was adjusted to 3.7 by addition of 2.5 M HCl.Then 12.86 wt %) (based on the weight of the emulsion) oftetraethylorthosilicate (TEOS) was added with mixing at 400 rpm for 4hours. After complete hydrolysis and condensation of the TEOS, asuspension of Core-Shell microcapsules was obtained having an averagevolume particle size of (Dv 0.5)=4.7 micrometers. The suspension wasthen diluted with water in order to obtain a solid content of 30%.Finally, 0.3% of 3-(trimethoxysilyl)-propyldimethylhexadecylammoniumchloride was added to the suspension to prevent gelation at 45° C.

Preparation of Suspensions of Microcapsules Containing Part B of theCurable Siloxane Composition.

A suspension of microcapsules containing Part B of the curable siloxanecomposition was prepared by dissolving 3.35 g of cetyl trimethylammonium chloride (CTAC) in 813.5 g of water. Then 600 g VINYL SILOXANEand 75 g of the SiH SILOXANE, was added with mixing at 400 rpm to theCTAC/water mixture to form 0/W emulsion. In this particular case anUltra-Turrax T25 Basic has been utilised for 90 seconds at 9500 rpm. Theresulting emulsion was then subjected to further shearing using an APV1000 Homogeniser at a pressure of 700 bars to produce a fine 0/Wemulsion having and average particle size (Dv 0.9) below 15 μm. The pHof the resulting emulsion was then adjusted to 3.7 by the addition of2.5 M HCl. Then 12.86% (based on the weight of the emulsion) oftetraethylorthosilicate (TEOS) was added with mixing at 400 rpm for 4hours. After complete hydrolysis and condensation of the TEOS, asuspension of Core-Shell microcapsules was obtained having had anaverage volume particle size of (Dv 0.5)=3.6 micrometers. The suspensionwas then diluted with water in order to obtain a solid content of 30%.Finally, 0.3% of 3-(trimethoxysilyl)-propyldimethylhexadecylammoniumchloride was added to the suspension to prevent gelation at 45° C.

The two aqueous suspensions containing the Microcapsules of the catalystand base blends as prepared above were then mixed together at a 1/1 w/wratio as based on the weight of each aqueous suspension.

Examples 3-6

Additional aqueous suspensions were prepared in a similar manner asExample 2 using the amounts of components and ingredients, as summarizedin Table 1 shown below.

These examples evaluated the effect of varying the SiH/Vi ratio in PartB and the overall SiH/Vi ratio in the curable siloxane composition (thatis Parts A and B combined), while maintaining a constant catalyst level(as determined by amount of elemental Pt).

Examples 7-8 (Comparative)

To further demonstrate the advantages of using microcapsules vs emulsionsystems to separate Parts A and B of the curable siloxane composition,two additional suspensions were prepared. In Example 7, Part B was usedas the core material in the microcapsules, while Part A was provided asan emulsion. In Example 8, Part A was used as the core material in themicrocapsules, while Part B was provided as an emulsion. The aqueoussuspension and emulsions used in these examples were prepared using thesame procedure as described above in Examples 1 and 2. The amounts usedin the examples are summarized in Table 1.

Examples 9-13 Preparation of Suspensions of Microcapsules ContainingPart A of the Curable Siloxane Composition Having DifferentTetraalkoxysilane Concentrations.

A suspension of microcapsules containing Part A of the curable siloxanecomposition was prepared by first dissolving 0.44 g of cetyl trimethylammonium chloride (CTAC) in 105.6 g of water. Then, a blend of 90.1 gVINYL SILOXANE and 2.8 g the CATALYST was added with mixing to theCTAC/water mixture to form an O/W emulsion. In this particular case anUltra-Turrax T25 Basic was utilised for 180 seconds at 9500 rpm. Theresulting emulsion was then subjected to further shearing using an APV1000 Homogeniser at a pressure of 700 bars to produce a fine 0/Wemulsion having an average particle size (Dv 0.9) below 15 μm. The pH ofthe resulting emulsion was adjusted to 2.9 by addition of 2.5 M HCl.Five aliquote of this emulsions have been taken: For example 9 to 13,2.5 wt %, 5 wt %, 7.5 wt %, 10 wt % and 12.5 wt % oftetraethylorthosilicate (TEOS) was respectively added to each aliquotswith mixing at 400 rpm for 4 hours. After complete hydrolysis andcondensation of the TEOS, a suspension of Core-Shell microcapsules wasobtained. The suspension was then diluted with water in order to obtaina solid content of 30%. Finally, 0.3% of3-(trimethoxysilyl)-propyldimethylhexadecylammonium chloride was addedto the suspension to prevent gelation at 45° C.

Preparation of Suspensions of Microcapsules Containing Part B of theCurable Siloxane Composition Having Different TetraalkoxysilaneConcentrations

A suspension of microcapsules containing Part B of the curable siloxanecomposition was prepared by dissolving 0.44 g of cetyl trimethylammonium chloride (CTAC) in 108.5 g of water. Then 80 g VINYL SILOXANEand 10 g of the SiH SILOXANE, was added with mixing at 400 rpm to theCTAC/water mixture to form 0/W emulsion. In this particular case anUltra-Turrax T25 Basic has been utilised for 90 seconds at 9500 rpm. Theresulting emulsion was then subjected to further shearing using an APV1000 Homogeniser at a pressure of 700 bars to produce a fine 0/Wemulsion having and average particle size (Dv 0.9) below 15 μm. The pHof the resulting emulsion was then adjusted to 2.85 by the addition of2.5 M HCl. Five aliquots of this emulsions have been taken: for example9 to 13, 2.5 wt %, 5 wt %, 7.5 wt %, 10 wt % and 12.5 wt % oftetraethylorthosilicate (TEOS) was respectively added to each aliquotswith mixing at 400 rpm for 4 hours. After complete hydrolysis andcondensation of the TEOS, a suspension of Core-Shell microcapsules wasobtained. The suspension was then diluted with water in order to obtaina solid content of 30%. Finally, 0.3% of3-(trimethoxysilyl)-propyldimethylhexadecylammonium chloride was addedto the suspension to prevent gelation at 45° C.

TABLE 1 Part A Part B Weight Vinyl Vinyl SiH ratio of Example siloxaneCatalyst TEOS siloxane siloxane TEOS suspension # (g) (g) (wt %) (g) (g)(wt %) A/B 3 88.5 2.8 12.86 90.5 4.8 12.86 1/1 4 88.5 2.8 12.86 72.2 1812.86 1/1 5 88.5 5.6 12.86 600 75 12.86 1/2 6 675.6 21 12.86 600 7512.86 2/1  7* 45 1.4 12.86 600 75 12.86 1/1  8* 675.6 21 12.86 40 512.86 1/1 9 90.1 2.8 2.5 80 10 2.5 1/1 10  90.1 2.8 5 80 10 5 1/1 11 90.1 2.8 7.5 80 10 7.5 1/1 12  90.1 2.8 10 80 10 10 1/1 13  90.1 2.812.5 80 10 12.5 1/1 *comparative example

The reactivity of the microencapsulated reactive blends and the qualityof the final film obtained was determined by coating the suspension (oremulsion) onto a silicon free Glassine paper. About 2 g of thesuspensions blend were coated with a 1.2 g/m² bar equipped with anautomatic film applicator (type 4340M1 from Braive Instruments). Theratio of the amount of silicon left onto the Glassine paper uponreaction before and after extraction with a good solvent for themonomers (e.g. in a 30 ml Methylisobutyl Ketone (MIBK) solution) allowsto plot the amount of extractable within the film during the reaction.The silicon concentrations onto the Glassine paper were determined byXRF using a Oxford Lab-X 3000.

The reactivity was calculated by measuring the slope of the extractableplot during the first 3 minutes after the coating of the Glassine paper.The lower values demonstrate higher reactivity. The quality of the filmis expressed by the extractable level measured 2 hours

The results for Examples 1-8 are summarized in Table 2.

TABLE 2 SiH/ Overall Vi SiH/Vi in Aging: None Aging: 3 Days RT Aging: 1Week 45° C. Aging: 2 months 45° C. Part curable Pt TEOS Reactiv-Extract- Reactiv- Extract- Reactiv- Extract- Reactiv- Extract- Bsiloxane (ppm) (wt %) ity (%) able (%) ity (%) able (%) ity (%) able (%)ity (%) able (%) Ex. 1* 6 2.8 79 0 58 11 65 28 Ex. 2 6 2.8 79 12.86 77 674 5 93 2 80 4 Ex. 3 2.5 1.27 79 12.86 75 13 60 30 Ex. 4 12 5.36 7912.86 26 52 Ex. 5 6 4.4 79 12.86 63 22 67 9 Ex. 6 6 1.84 79 12.86 80 582 4 70 6 68 9 Ex. 7* 6 2.8 79 12.86 30 65 Ex. 8* 6 2.8 79 12.86 67 29Ex. 9 6 2.8 79 2.5 45 28 Ex. 10 6 2.8 79 5 20 8 Ex. 11 6 2.8 79 7.5 13 6Ex. 12 6 2.8 79 10 11 6 Ex. 13 6 2.8 79 12.5 7 4 *comparative example

1. An aqueous suspension of silicate shell microcapsules wherein a firstportion of the silicate shell microcapsules contain as a core Part A ofa curable siloxane composition comprising; a) an organopolysiloxanehaving at least two silicon-bonded alkenyl groups per molecule, b) ahydrosilylation catalyst, and a second portion of the silicate shellmicrocapsules contain as a core Part B of the curable siloxanecomposition comprising; c) an organohydrogensiloxane having an averageof greater than two silicon bonded hydrogen atoms (SiH) per molecule. 2.The aqueous suspension of claim 1 wherein Part B of the curable siloxanecomposition further comprises a) the organopolysiloxane having at leasttwo alkenyl groups.
 3. The aqueous suspension of claim 2 wherein theamount used of components a) and c) provides a molar ratio of the SiHunits of the organohydrogensiloxane to the alkenyl groups in theorganopolysiloxane that is from 1 to
 4. 4. The aqueous suspension ofclaim 3 wherein the molar ratio of the SiH units of theorganohydrogensiloxane to the alkenyl groups in the organopolysiloxaneused in Part B of the curable siloxane composition is from 3 to
 10. 5.The aqueous suspension of any of the above claims wherein theorganopolysiloxane having at least two alkenyl groups comprises at leasttwo siloxane units represented by the average formulaR²R_(m)SiO_((4-m)/2) wherein R is a hydrocarbon group containing 1 to 20carbon atoms, R² is a monovalent alkenyl aliphatic group, and m is zeroto
 2. 6. The aqueous suspension of claim 5 wherein theorganopolysiloxane having at least two alkenyl groups has the averageformula;CH₂═CH(Me)₂SiO[Me₂SiO]_(x′)Si(Me)₂CH═CH₂CH₂═CH—(CH₂)₄-(Me)₂SiO[Me₂SiO]_(X′)Si(Me)₂-(CH₂)₄—CH═CH₂, orMe₃SiO[(Me)₂SiO]_(x′)[CH₂═CH(Me)SiO]_(x″)SiMe₃ wherein Me is methyl,x′≧0, and x″≧2.
 7. The aqueous suspension of claim 1 wherein theorganohydrogensiloxane comprises the average formula; (R³₃SiO_(1/2))_(a)(R⁴ ₂SiO_(2/2))_(b)(R⁴HSiO_(2/2))_(c) wherein R³ ishydrogen or R⁴, R⁴ is a monovalent hydrocarbyl containing 1 to 10 carbonatoms, a≧2, b≧0, c≧2.
 8. The aqueous suspension of claim 7 wherein theorganohydrogensiloxane is selected from a dimethyl, methyl-hydrogenpolysiloxane having the average formula;(CH₃)₃SiO[(CH₃)₂SiO]_(b)[(CH₃)HSiO]_(c)Si(CH₃)₃ where b≧0, and c≧2. 9.The aqueous suspension of claim 1 wherein the hydrosilylation catalystis an elemental platinum group metal having a concentration of 1 to 500ppm in the curable siloxane composition.
 10. The aqueous suspension ofclaim 1 wherein the silicate shell microcapsules are obtained by; I)mixing an oil phase containing Part A or Part B of the curable siloxanecomposition and an aqueous solution of a cationic surfactant to form anoil in water emulsion, II) adding a water reactive silicon compoundcomprising a tetraalkoxysilane to the oil in water emulsion, III)polymerizing the tetraalkoxysilane at the oil/water interface of theemulsion to form a microcapsule having a core containing either Part Aor Part B of the curable siloxane composition and a silicate shell, IV)combining the microcapsules containing Part A of the curable siloxanecomposition with the microcapsules containing Part B of the curablesiloxane composition.
 11. The aqueous suspension of claim 10 wherein thetetraalkoxysilane is tetraethoxysilane.
 12. The aqueous suspension ofclaim 10 wherein the water reactive silicon compound further comprises(CH₃O)₃SiCH₂CH₂CH₂N⁺(CH₃)₂(CH₂)₁₇CH₃Cl⁻.
 13. A process for preparing asuspension of silicate shell microcapsules comprising; preparing a firstsuspension of silicate shell microcapsules by I) mixing an oil phasecontaining Part A of a curable siloxane composition comprising; a) anorganopolysiloxane having at least two alkenyl groups, b) ahydrosilylation catalyst, and an aqueous solution of a cationicsurfactant to form an oil in water emulsion, II) adding a water reactivesilicon compound comprising a tetraalkoxysilane to the oil in wateremulsion, III) polymerizing the tetraalkoxysilane at the oil/waterinterface of the emulsion to form a microcapsule having a corecontaining the oil and a silicate shell; preparing a second suspensionof silicate shell microcapsules by I) mixing an oil phase containingPart B of a curable siloxane composition comprising; c) anorganohydrogensiloxane having an average of greater than two siliconbonded hydrogen atoms (SiH) per molecule and an aqueous solution of acationic surfactant to form an oil in water emulsion, II) adding a waterreactive silicon compound comprising a tetraalkoxysilane to the oil inwater emulsion, III) polymerizing the tetraalkoxysilane at the oil/waterinterface of the emulsion to form a microcapsule having a corecontaining the oil and a silicate shell; and mixing the first and secondsuspensions together.
 14. The process of claim 13 wherein the weightratio of the first suspension mixed with the second suspension variesfrom 0.9 to 1.1.
 15. A cured siloxane composition obtained by curing thecomposition of claim 1.